The present invention relates to method and apparatus for controlling the slide of an optical pickup equipped in an optical disk device.
A conventional optical disk device is shown in FIG. 1. The device reproduces signals recorded on an optical disk 1 through an optical pickup 2, a R/F unit 3, a digital signal processing unit 4, and a decoder 5.
The optical pickup 2 reproduces recorded signals from an optical disk 1; the R/F unit 3 combines signals reproduced by the optical pickup 2 and outputs servo error signals (discussed below) and binary signals; the digital signal processing unit 4 processes the binary signals received from the R/F unit 3 to retrieve digital data; and the decoder 5 decodes the retrieved digital data into original data.
The optical disk device also tracks data on the optical disk 1 by controlling a sled motor 10 and a spindle motor 11. The sled motor 10 slides the optical pickup 2 across tracks of the optical disk 1 and the spindle motor 11 rotates the optical disk 1.
The control is accomplished through the R/F unit 3, a servo unit 6, and a driver 7. As mentioned above, the R/F unit 3 outputs servo error signals. The servo unit 6 receives the servo error signals from the R/F unit 3 and outputs servo control signals to the driver 7. The driver 7 in turn outputs signals to control the sled motor 10 and the spindle motor 11.
The entire operation is supervised by the microcomputer 8. A memory 9 is used by the microcomputer 8.
The operation of the conventional optical disk device is as follows. Once the optical disk 1 is inserted into a disk tray (not shown), the optical disk 1 is clamped by a clamping means (also not shown). Then the driver 7, under the control of the servo unit 6, applies a driving current to the spindle motor 11 to rotate the optical disk 1 at a constant or variable speed.
To reproduce signals recorded on the optical disk 1, the optical pickup 2 uses a laser diode (LD) to form a laser beam spot on the recorded layer of optical disk 2. The laser beam is reflected to photo diodes (PD) and converted to electrical signals. The R/F unit 3 takes in these electrical signals and extracts the recorded binary signals. The digital signal processing unit 4 restores the extracted binary signals into digitally modulated data, and the decoder 5 demodulates the digital data from the digital signal processing unit 4 into original digital data.
To control tracking, the R/F unit 3 also generates servo error signals, including a tracking error signal, based on the converted electrical signals from the optical pickup 2. Using the tracking error signal, the servo unit 6 generates servo control signals, which is then outputted to the driver 7. The driver 7 applies electric currents to an actuator to control the movement of an object lens to follow a target track on the optical disk 1.
However, under such tracking control system, the center of the object lens may deviate from an optical axis of the target track. For example, as shown in FIG. 2A, the object lens may deviate to a small extent from the optical axis. On the other hand, the object lens may deviate greatly to the maximum allowable swing limit, as shown in FIG. 2B.
If the deviation approaches the maximum allowable swing limit, then as shown in FIG. 2C, the servo unit 6 detects such critical deviation from the magnitude of the tracking error signal and drives the sled motor 10 to move the optical pickup 2 to correct the deviation. The optical pickup 2 is moved until the magnitude of the tracking error signal is reduced to zero or within a predetermined small range as shown in FIG. 2D.
While the optical pickup 2 slides to the right as shown in FIG. 2C, the actuator enclosing the object lens is also swung to the left by tracking control of the servo unit 6, so that the center of the object lens coincides with the optical axis. When the center of the object lens so coincides, then the object lens is stabilized.
However, if an excessive load is applied to the sled motor 10 or if the driving characteristics of the sled motor 10 are not within acceptable load range, the reproduction may be unreliable, tracking may be difficult to control, and data reading may fail.
To compensate, an entire gain of the slide servo could be increased. But the ability to track and reproduce data from an eccentric disk would be compromised.
Also if an excessive load is applied to the sled motor 10 or if the driving characteristics of the sled motor 10 is not uniform within acceptable load range, the object lens deviation may not be corrected quickly enough. This may cause an over-shifting of the object lens or the object lens may oscillate freely. These are fatal errors that will halt the device operation.
It is an object of the present invention to provide a servo control method and apparatus capable of detecting a reproduction speed and amount of deviation of an object lens from an optical axis, and compensating to return the object lens to the optical axis even if a heavy load is applied to the driving mechanism.
It is another object of the present invention to provide a servo control method and apparatus capable of maintaining the center of an object lens around the optical axis within a predetermined range. This predetermined range is narrower than a maximum movable range of the object lens.
A servo control method of an optical disk device according to the present invention detects a magnitude of deviation of an object lens from an optical axis of an optical track based on a deviation error signal in normal disk reproduction mode; checks whether the deviation is out of a predetermined range which is narrower than a maximum movable range of the object lens, adjusts a gain for amplifying the deviation error signal, and, if the detected magnitude is out of the predetermined range, applies the deviation error signal amplified by the adjusted gain to a motor for sliding an optical pickup, so that the object lens returns to the optical axis.